Interpretive Summary: Plant explorations have collected seeds from wild apple (Malus orientalis) trees in Georgia, Armenia, Russia, and Turkey. These seeds have been planted at the USDA-ARS Plant Genetic Resources Unit (PGRU) in Geneva, NY. Seedling trees have been evaluated for resistance to critical diseases such as fire blight, apple scab, and cedar apple rust. Six of the trees from Armenia were found to be resistant to all three diseases. The diversity of 280 individuals from Georgia and Armenia was assessed using seven microsatellite markers. We identified a set of 27 trees that captured 93% of the allelic diversity in the 776 M. orientalis trees at the PGRU. This core collection will be maintained in the field in Geneva, NY.

Technical Abstract:
Seeds were collected from wild Malus orientalis (Uglitzh) trees during recent plant collecting explorations to Armenia, Georgia, Turkey, and Russia. Disease resistance and genotypic data are available for the 776 M. orientalis seedling trees in the field collection at the USDA-ARS Plant Genetic Resources Unit (PGRU) in Geneva, NY. Six individuals from Armenia exhibit resistance to fire blight (Erwinia amylovora Burrill), apple scab (Venturia inaequalis Cooke) and cedar apple rust (Gymnosporangium juniperi-virginianae Schwein). The genetic diversity, based on results from seven microsatellite markers, was assessed for 280 individuals from Armenia and Georgia. A total of 106 alleles were identified and the average gene diversity ranged from 0.47 to 0.85 per locus. Genetic differentiation among sampling locations within Georgia and Armenia was greater than that found between the two countries. We have identified a core set of 27 trees based on the genotypic data to represent the 776 M. orientalis collection at the PGRU. These trees include individuals from each of the four countries and capture 93% of the alleles identified in M. orientalis using the seven microsatellite markers. These trees in the core collection will added to the main field collection at the PGRU.